 Green Mountain Energy Company purchases wind power from turbines on a farm near Garrett, Pennsylvania, for sale to customers in Pennsylvania and New Jersey. (Credit: Green Mountain Energy Company) |
People have harnessed the power of the wind for centuries. In the first half of the 20th century, windmills dotted the U.S. countryside, pumping water, grinding grain, and generating small amounts of electricity to light rural farmhouses. Today, wind power is the fastest growing energy source in the world. By the end of 2000, total world wind capacity was about 17,000 MW, enough to generate about 34 billion kWh a year of electricity. That's enough electricity to power New York City.
Wind is a clean, renewable energy technology that is becoming increasingly popular with utility customers and policy makers. In response, utilities are developing new wind power plants consisting of many wind turbines. As additional wind power becomes available, more electricity customers are signing up to invest in clean, sustainable wind power. As concerns about global warming increase, utilities and their customers may support an even more prominent role for wind in meeting the nation's needs for new power generation. Many states are implementing policies such as renewable portfolio standards and net metering to hasten the development of their wind resources.
How It Works
Today's wind turbines are a much more efficient technology than windmills of the past. They have fewer blades, usually two or three, that are aerodynamically designed to capture the most energy from the wind. When the wind blows, a pocket of low-pressure air forms on the downwind side of the blade pulling the blade toward it, causing lift. This lift force causes the rotor to spin, which turns a generator that makes direct current electricity (see diagram). Sophisticated power electronics convert the direct current electricity into the high quality, alternating current electricity transmitted through the power grid.
 Components of a wind turbine |
As wind speeds increase, the amount of electricity generated increases exponentially. Because faster, less turbulent winds are found higher off the ground, new utility-scale wind turbines are normally placed on towers at least a hundred feet tall. At high wind speeds, a controller on the turbine shuts it down so turbine components won't be damaged by high winds.
See an animation of a wind turbine in action.
Wind is an indirect form of solar power because sunlight causes temperature variations in the Earth's atmosphere. Major winds, such as the trade winds and jet stream, are created by the uneven heating of the Earth's atmosphere and modified by the planet's rotation. Closer to the surface, winds are formed by temperature differences between mountains and valleys or coastal and inland regions. Winds are also caused by pressure differences between large air masses and the storms generated at the boundaries between air masses, called fronts.
Advantages
The United States has enormous wind energy potential. Six percent of the nation has excellent wind resources that could provide more electricity than the entire country used in 2000.
Wind power is affordable. Electricity from wind typically costs between 4 c/kWh and 6 c/kWh, a seven-fold decrease since 1980. New blade designs, which have increased wind turbine performance by 30% over the past decade, are helping make wind power one of the most cost-competitive renewable technologies. Researchers believe that additional technological improvements could cut prices for wind-generated electricity by another 30% to 50%.
Wind power is versatile, adaptable, and readily available. New utility wind plants can be constructed in less than a year. For stand-alone applications, wind turbines can be combined with photovoltaic panels, batteries, and diesel generators to ensure that electricity is available whenever it is needed.
Wind energy provides more jobs per dollar invested than any other energy technology.
Wind turbines add value to land without interfering with other uses such as cattle grazing or farming. The Union of Concerned Scientists reports that a Midwestern farmer hosting a wind plant can expect extra earnings of about $40 per acre, increasing his return on the land by 30% to 100%.
Homeowners and businesses in windy rural areas can use wind turbines to reduce their electric bills. In many states, consumers who own grid-connected wind turbines that produce more electricity than they need can sell that extra electricity back to their utility company. Some states offer tax incentives and other support for wind energy.
Wind power plants offer advantages to utilities. They are reliable. Even if several turbines in a plant are down for maintenance, the flow of electricity into the grid continues uninterrupted so long as the wind is blowing. Wind power plants also produce clean energy. They produce no emissions and no hazardous wastes. Wind generation displaces fossil fuels, thereby reducing pollution, acid rain, and emissions of greenhouse gases.
In developing countries, wind turbines can generate electricity for refrigeration, lighting, and an improved quality of life to people in remote areas who have never had electricity. Wind energy also gives them the chance to industrialize in an environmentally sound manner.
Wind's many advantages have made it the fastest growing source of energy in the world since 1990. Thanks to dramatic improvements in wind technology, wind power is growing, on average, at a rate of 30% per year.
Disadvantages
Utilities can find it challenging to integrate wind power into their generation mix. Unlike traditional power sources, the wind is intermittent. How can utilities plan for power that is only available when the wind blows? Researchers are currently working to develop better ways of forecasting the wind so that utilities could actually power down some conventional gas turbines with confidence in times of high winds, thus conserving natural gas.
Stand-alone wind turbines must use a backup power system for when the wind stops blowing. Turbines not connected to the grid can charge batteries for backup power. Should the batteries run low, a backup generator can charge them up again or supply power as needed. However, battery-charging systems and backup generators can significantly increase the costs of a wind system.
Zoning and other land use regulations can be problematic for individuals wanting to install turbines. There may be additional expense for power conditioning equipment to ensure the turbine won't interfere with grid power. Many states also require insurance, which can be expensive.
Applications
Applications of wind power range from small stand-alone systems to utility-scale wind power plants. With improved technology and lower cost, wind is growing in popularity — both for utilities and for their customers. Many U.S. utilities now offer wind power as a choice to consumers interested in buying sustainable, clean energy.
Utility-scale wind generation is well suited to the Great Plains and Upper Midwest regions of the United States. Both areas have good wind resources and wide-open spaces. There are large utility wind power plants in California, Colorado, Iowa, Kansas, Minnesota, Oregon, Texas, Washington, and Wyoming. Turbines used in these wind power plants range in size from 50 kW to 2 MW.
European nations — including Denmark, Germany, the Netherlands, Spain, and Sweden — emphasize distributed wind generation. These heavily populated nations have far less open land for wind power than the United States. For this reason, they are pioneering distributed generation with large, multimegawatt turbines. These nations have also begun experimenting with offshore wind turbines. They are installing wind turbines in shallow water near the coastline to take advantage of strong, offshore winds.
In the United States, ranchers and farmers use wind to generate electricity and pump water. Today's grid-connected small turbines (sized between 400 W and 50 kW) give rural residents a hedge against power fluctuations that can occur at the end of weak transmission lines. Clusters of small turbines can be connected to a utility power grid for distributed generation.
Stand-alone small turbines are often far less expensive than extending a power line in remote areas, which can cost up to $10,000 per mile. Small turbines, sized below 50 kW, can be used for homes, telecommunications, or water pumping.
Small wind turbines made by U. S. companies already bring clean power to remote villages in Asia, Indonesia, Mexico, Morocco, and South America. Wind systems help pump water for drinking and irrigation. In combination with other renewable technologies, such as solar photovoltaics, batteries, or back-up diesel generators, hybrid wind systems power small electric grids. Local residents use these grids for lighting, television, radio, ice making, refrigeration, grain grinding, battery charging, powering local industries, and for telecommunications.
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